Wireless and portable electronic devices, sensors, and cameras need independent power supplies to enable operation in areas where the electrical grid is not easily accessible. Currently, batteries are used to power the majority of the devices, which are finite energy sources that are susceptible to environmental conditions such as high or low temperatures. The shortcomings of these energy sources limit the operating time of the devices. As a result, the batteries have to be frequently recharged or replaced to extend the operating time of the devices. Recharging typically needs access to the grid and to power conversion electronics. The alternative method of battery replacement is a significant cost factor and raises environmental concerns.
The most viable alternative to batteries is power harvesting from the environment. Typically, wind or solar energy are used. However, these power harvesting devices have to be rather large and will not work when there is no light (at night) or wind. Other alternatives such as vibration or thermal energy harvesting are limited to very small application areas where vibrations or thermal gradients are present. An alternative would be to utilize the oxygen in air to oxidize fuel compounds produced by ubiquitous plants. These fuels consist of carbohydrates that have been produced via photosynthetic or metabolic pathways.
The utilization of such fuels to produce electrical power has been described before. Fuel cells have been constructed that use the nutrients directly or with the help of electron transfer mediators. The problems with such fuel cells are that the nutrients are in direct contact with either the catalysts or the mediator compounds, which results in catalyst or mediator deactivation/poising. As a result, the operating time of such devices is very limited. For example, U.S. Pat. No. 7,160,637 discloses the utilization of sugars such as glucose to power a direct conversion microbial fuel cell. However, the total performance duration displayed is less than 5 hours. Such a fuel cell has also been disclosed in U.S. Pat. No. 6,500,571, where redox enzymes have been used as electron transfer mediators.
Organic waste has also been used to produce hydrogen containing gases. For example, in U.S. Pat. No. 5,464,539, waste streams containing cellulose and sugar complexes are utilized as a feed stream for micro-organisms to produce mixtures of hydrogen and carbon dioxide. Another process described in U.S. Pat. No. 6,984,305 converts solid waste in an anaerobic reaction with the help of microorganisms and an applied voltage into a gas containing hydrogen. Similarly, U.S. Pat. No. 7,033,822 discloses a process to convert organic waste materials into high purity hydrogen by adding a gas purification device to separate the gas mixture produced by an anaerobic decomposition reaction. In addition, a method for hydrogen production from biodegradable feedstock using a two-stage anaerobic bioreactor has been described in U.S. Pat. No. 6,887,692. Light and photosynthetic bacteria are used in this process to produce the gas.
An exemplary embodiment of the present invention utilizes nutrient containing liquids from living plants as the fuel material. The device interfaces with the plant for extended periods and does not significantly impede natural functions, which keeps the plant alive. Related methods to form such an interface are techniques used to distribute nutrients and medicine to living plants. For example, in U.S. Pat. No. 6,311,429, a tree implant device is disclosed that supplies medication into the phloem layer for distribution within trees. The device makes use of the sap pressure within trees to squeeze medication from the device over an extended period of time. This naturally occurring sap pressure can be utilized as the fuel delivery mechanism in the present invention.
The tree implant device of the current invention introduces a new class of energy harvesting device in which energy in the form of plant nutrients is utilized for the production of hydrogen. The invention solves the problems discussed above and provides advantages that are not possible with other power harvesting methods. A discussion of the features and advantages of the present invention is deferred to the following description.